Thyroid Flashcards
where does the thyroid sit
C5-T1
in the anterior portion of the neck
what is its relations
ant: pre-tracheal muscles + skin
post: four parathyroid glands, one at each upper pole and one at each lower pole of each lobe. behind the middle portion is the isthmus
sup: larynx
what is it lined with
cuboidal epithelium
what does the thyroid follicles produce
thyroglobulin
what does the central cavity store and secrete
colloid
thick sticky protein which contains thyroglobulin attached to iodine, which helps in the hormone production
what surrounds the thyroid follicles
parafollicles which secrete calcitonin
what do thyroid follicles do
manufacture, store and secrete hormones
what does thyroglobulin contain
tyrosine which binds with iodine to produce T4 and T3 in iodine trapping
T4
two tyrosine moles and 4 iodine [major hormone secreted]
T3
two tyrosine and three iodine
formed mainly in the conversion at target tissues
what does the thyroid wrap around
the thyroid cartilage
what is the blood supply
highly vascular
supplied by the R + L superior thyroid arteries which are branches of the external carotid arteries
R+ L inferior thyroid arteries are branches of the subclavian
isthmus -> thyroid ima artery os a branch from the external carotid
venous: via a network at the surface of the gland: thyroid veins which are drawn into the internal jugular vein
is it a rare cancer
yes
aetiology
areas of nuclear disaster
previous RT
autoimmune conditions
genetic factors
what are the five pathology types
papillary
follicular
anaplastic
medullary
malignant lymphoma
what are the differentiated types
papillary and follicular
describe papillary
common, slow growing, finger like projections of stroma
describe follicular
occur in patients with goitre
appears solid, solitary, well circumscribed mass
minimal or widely invasive
what can be tracked with differentiated tumours
hormone production, as they produce thyroid hormones
what tumours are undifferentiated
anaplastic and medullary
describe anaplastic
giant or spindle cell
rapid growth and radioresistant
describe medullary
arises from para-follicular cells
slow growing
can contain calcium [if not present it indicates a more aggressive tumour]
describe malignant lymphoma
non hodgkins
varies from high to low grade
what is a T1a
solitary <1cm
T1b
multifocal lesion largest <1cm
T2a
solitary <2cm
T2b
multifocal largest is <2cm
T3
lesions >4cm confined within a capsule
T4
extension beyond the capsule
what is the follicular spread
via the blood stream to lung and bone
likely to metastasise
what is papillary spread
regional lymphatics
via deep chain, supraclavicular and paratracheal chain
immobilisation is important for these tumours
what is the anaplastic spread
local invasion = neck growth
met to lung, liver and bone early
what is the medullary spread
via lymph node and blood stream
high met potential
deposits at the mediastinum are common
what is the lymphoma spread
via local LN
recurrence in the GI tract is common
what happens if the thyroid capsule is breached
then the trachea, larynx, recurrent laryngeal nerve and skin can be involved
how do all of them spread
along the lobe of origin, before spreading to the other lobe via the isthmus
how do PC present
solitary mass in one lobe or multiple lesions throughout the gland
enlarged neck nodes [1/3 = bilateral]
FC presentation
relate to met spread [jaundice, dysponea (10%) and pathological fracture]
APC presentation
rapid and large
nerve pain or vocal palsy due to involvement of the recurrent laryngeal nerve
stridor or dysponsea = tracheal compression
dysphagia = oesophageal compression
MC presentation
diarrhoea = secretion of prostaglandins
what produces the pyramidal lobe
cell remnants along the tract, lateral parts from the cells in the pharyngeal floor elongates then detaches
what does calcitonin do to calcium levels
decreases them
what investigations take place
full medical history
examination
indirect laryngoscopy
radiography
FNA
radioactive iodine uptake
what happens at the full medical history stage
previous neck RT
family history of thyroid or endocrine disease
previous disease
what happens at the examination
neck palpation [masses or scars from previous surgery]
differentiated masses move whilst swallowing whereas undifferentiated are fixed
what is the indirect laryngoscopy for
to check for vocal palsy, involvement of the recurrent laryngeal nerve
what is done at the radiography stage
plain x ray = calcium deposits/ tracheal compression
US = size and location of suspicious nodules prior FNA
FNA, is it the most reliable
yes, in distinguishing between benign and malignant
how can these be managed
the management is unclear
relapse is a potential due to under and over treating the patient
most patients are eythyroid which means they have a normal functioning thyroid gland and hormones
what are para-follicles also classed as
C-cells
they have a good blood supply
what gland and nerve are closely associated
para-thyroid gland and the recurrent laryngeal nerve
what tumours arise in the follicular cells
anaplastic
follicular
papillary
what tumour arises in the parafollicles
medullary
why is a incomplete excision sometimes done
some extra-capsular tissue is left to minimise damage to the recurrent laryngeal nerve which runs behind the the thyroid tissue as well as the pituitary gland remaining in tact
what is the physiology behind the functioning of the hormones etc
Thyrotropin - Releasing Hormone [TRH]
small tri peptide formed in hypothalamus
flows along the neruones to the hypophyseal portal system which supplies the anterior pituitary gland
TSH is released after TRH stimulation
TSH releases T3+T4 from thyroid
as T3+T4 levels increase, TRH decreases, decreasing the TSH secretions
what do T3+T4 regulate
weight, metabolism, internal temp, skin and hair
indications for adjuvant RT
incompletely excised or inoperable, well differentiated with inadequate I-131 uptake
medullary carcinoma
indications for primary or adjuvant to surgery
anaplastic carcinoma to improve local control
not curative
what does advanced disease indicate
recurrent or mets
how are differentiated tumours managed
surgery
EBRT
describe surgery for differentiated tumours
treatment of choice
total thyroidectomy
partial thyroidectomy = leaving 2-3g to influence T3/T4 production
trachestomy = advanced
thyroid ablation is common after surgery
EBRT for differentiated
HFS supine
CT localisation
shell
chin extended
IMRT uses dose painting for MC
concave PTV, IMRT, 60Gy in 30
side effects to RT
mucositis
erythema
dry desquamation/ MDS
weightloss
how are anaplastic tumours managed
radio-resistant therefore palliative RT
AP POP
30Gy in 10
can prevent asphylation due to aggressive tumour
what is the prognosis for PC/FC
80-90% in 10 years
what is the prognosis for AC
poor
6 months survival
what is the prognosis for MC
worse prognosis however if detected early long term survival is possible
when is hormone replacement given
always
oral thyroxine for the rest of their life
suppresses TSH production for pituitary gland and prevents hypothyroidism
describe the location of the parathyroid
descends along with the thyroid
two superior at upper pole
two inf
angle of mandible to aortic arch
if enlarged it extends to the mediastinum extension
what do the parathyroids do
produce, secrete and store para-thyroid hormone
what does PTH do
regulates calcium and phoshorous in the blood
increases osteoclastic activity
increasing Ca release
increases tubular reabsorption of Ca
increases intestinal reabsorption of Ca
what happens when the parathyroid gland is removed
PTH levels fall = decrease in Ca levels = increased excitability of neuromuscular tissue = tetancy [twitching]
what is the half life for iodine
8 days
what characteristic do the tumours have which undergo radioactive ablation
act in a similar way to normal thyroid
tumours >4cm
gross extrathyroid extension and mets
what are the risks to iodine ablation
transport source
administration
transport patient
in patient room and surrounding area
waste management and disposal
patient leaving the hospital
readmission of the patient whilst radioactive
post therapy scanning procedures
why might repeat surgery/ablation be needed
due to it being difficult to ablate lage amounts of normal thyroid
where is I-131 found
internalised within the cell, beta radiation occurs within the cell
adjacent cells are in the pathway of 0.9mm so are also irradiated
what are the systems of work
control access
controlled areas
signage
no visitors
no items left in the room
time distance shielding
training
EPDs on entry, ALARP
what is the procedure
consent
not for pregnant etc
low iodine diet 2 weeks prior [ensure high uptake of I-131]
salt, cough mixture, seafoods, kelp, medications
avoid iv contrast for 2 months prior
TSH levels must be high, TSH IM injections might be given
dose is decided by the MDT
what are the doses given
early = 1.1GBq + 3.7 GBq
late = 3.7Gbq - 5.5
absorption occurs in the first two hours
what is said regarding pregnancy etc after treatment
not to get pregnant/father a child for 6 months
stop breast feeding for 8 weeks
limit contact to children and pregnant women
what can happen in the first 24 hrs
vomitting
what hazard is in the first 48 hours
urine hazards [highest risk]
what hazard happens for approx a week
sweating
patient bodily fluids
what are the side effects to radioactive ablation
bone marrow depression = anaemia, leukopaenia, thromocytopaenia
nausea
neck swelling
taste changes
sialoadenitis = dry mouth
lung fibrosis + acute pneumonitis
radiation cystitis
gastritis
bleeding
management for ablation
good hydration and laxative
what are the late effects
dry mouth
abnormal taste
laryngeal oedema
swelling, restricted neck movement
high risk of miscarriage after a year
transient ovarian failure
male infertility
pulmonary fibrosis with lung mets
what happens at the follow up
diagnostic I-123 scan, 3-6 months after for functioning uptake
probe with a sodium iodide crystal uptake at 2-4 hours and 24 hours
if no uptake the patient might need a full body radionuclide scan to see if there is any functioning mets
what does low uptake on the scan indicate
hypothyroidism
thyroiditis
recent contrast
exogeneous iodine
antithyroid medication
foods which compete in iodine trapping
ectopic thyroid tissue
what happens if further ablation is required
- a dose of 5.5GBq is normally given but can range from 3.7-7.4
- risk dose to lung is undetected micro mets
- 1-3 treatments but 6 is the max given
follow up
life long follow up
detect recurrence
monitor TSH suppression
detect and manage hypercalciaema
what is the prognosis for ablation treatment dependent on
well differentiated = 5-20% met development
age, size, grade
extrathyroid spread,
distant met spread
lung -> bone -> liver and brain
children <10 years
what does I-131 do
it travels to the functioning thyroid tissue, where a high dose is given, a low dose is found everywhere else
when all normal thyroid tissue is destroyed the malignant tissue becomes stimulated by TSH and begins to function to replace the missing thyroid
what is the MBq of the tracer
185
what is thyrotoxicosis
clinical hyperthyroidism
- overstimulation of TSH receptors
- excess thyroid hormone in body = T3/T4
what % is graves disease of thyrotoxicosis
60-85%
what is the remainder % of thyrotoxicosis
nodular thyroid disease
what are the tests which are carried out for thyrotoxicosis
- Free T4
- Free T3
- TSH
- thyroid scan I-123 or Tc-99m
- thyroid uptake I-131
- graves disease is increased
- toxic nodular goitre normal or mildly increased
signs and symptoms for thyrotoxicosis
increased metabolism
raised T3/T4 in blood
agitation
palpitations
diarrhoea
loss of libido
intolerant to heat
fatigue
weakness
sweating
weightloss
protrusion of the eye
fatal cardiac arrhythmia
treatment for thyrotoxicosis
surgery
antithyroid drugs
beta blockers
RAI 131 - treatment of choice, highly effective, easy and safe
describe radioiodine therapy
can be ablative or non ablative
stop meds
dose = thyroid gland x 100-180MiCi/ gm
- 185-555MBq
outcome at 4-8 weeks
increasing the dose increases the change of hypothyroidism which also increases with time
what do large doses of iodine 131 do
minimise potential morbidity quickly which results in certain hypothyroidism
what is the process of radioiodine therapy
order capsule 72 hours prior
measure activity within 10% of prescribed dose
stop antithyroid med 3 days prior
remove dentures
dont chew
hot drink after administration or water
who is not given RIT
pregnant women
<10 years
what are the pre-cautions for thyrotoxicosis RIT
cardiac arrest
contact RPA or RPS
dont do mouth to mouth
gloves and apron
film badge
shielding for crash team
death enclosed fully in plastic bag
when should they avoid public transport
> 400 MBq
should avoid crowds as well
what advice should be given
should sleep away from partner
wear kitchen gloves
when should you stay away from work
> 400MBq
when should you avoid contact with others
adults: >150
children: >30
when should you remain in hospital
> 800MBq
what are the issues with RIT
vomiting
If disease is not controlled then further doses are given
- 50% patients feel better after 3 months
- 50% need 2/3 treatments to get desired control
subsequent hypothyroidism is treated with thyroxin
risk: leukaemia, thyroid cancer, gene mutations in repro cells
post iodine follow up
at 6 weeks, 12 weeks [free test T4 + TSH]
6 months, 1 year and then annual life long follow up
what are hypothyroid symptoms
over weight, sluggish, leathery skin,
patients with thyrotoxicosis what percent become hypothyroid after 2 years
50
what increases the risk of a hypothyroid
small goitre size
family history of autoimmune thyroid disease
what are the signs of hyperthyroidism
twitching
palpations
warm skin
red palms
loose nails
urituria
patchy hair loss
eye problems
symptoms of hyperthyroidism
hyperactivity
mood swings
difficulty sleeping
tired
frequency
persistent thirst
itchiness
loss of interest in sex
what is graves opthalmopathy
overproduction of thyroid hormones, enlarging the fat pads pushing the eyes forward increasing pressure on the bony orbit affecting the extra-ocular muscles, can lead to blindness
what is the dose prescription for graves opthalmopathy
20Gy in 10 [very responsive]
what is the technique for graves opthalmopathy
POP
angle 5% posterior taking away from the lens
1/2 beam block to only treat the back of the eye
50% isodose to the pituitary gland
what is the TV for graves opthalmopathy
orbit fat + extraocular muscles
want to treat tissues behind the eye
position for RT for graves opthalmopathy
supine
shell
CT
what are the side effects to RT for graves opthalmopathy
pressure increase = inflammation
dry eyes
what is thyrotoxicosis
clinical state associated with
the raised levels of circulating T3/T4, increased levels of thyroid hormones
